This invention relates generally to a method and apparatus for providing fuel to a combustion prechamber and, more particularly, to a method and apparatus for providing a hydrogen enriched reformed fuel to a combustion prechamber.
Internal combustion engines are typically configured to introduce an amount of fuel of some type into a main combustion chamber, in which the fuel is ignited to provide power to operate the engine. Various kinds of fuel are used with varying degrees of ignition and combustion properties. One example of fuel is natural gas, which has a high octane number and thus provides a substantial resistance to engine knock. However, when natural gas is introduced as a lean mixture, i.e., mixed with oxygen, for the purpose of reducing noxious emissions, the lean natural gas mixture does not ignite as well as desired.
A common method for overcoming the problem of poor ignition of lean fuel mixtures is to deliver a small amount of a rich mixture of fuel into a combustion prechamber. The fuel in the prechamber is then ignited and the resultant combustion flame is diverted into the main chamber to ignite the leaner fuel mixture in the main chamber.
It has also been found that a hydrogen enriched fuel, for example a reformed fuel, introduced into the prechamber provides for increased ignition properties in the prechamber. For example, in U.S. Pat. No. 5,611,307, Watson discloses a system which introduces hydrogen into a prechamber, either directly or by way of reformed fuel. The rich hydrogen mixture, which has an equivalence ratio in the range of 1.2 to 7 times stoichiometric, is then ignited. The resultant flame is diverted into the main chamber for combustion of the primary fuel.
Although the rich hydrogen prechamber mixture disclosed by Watson may increase combustion efficiency in the main chamber, the rich mixture results in highly increased temperatures within the prechamber. For example, the temperature at a prechamber tip, i.e., the portion of the prechamber allowing entrance of the flame into the main chamber, may be about 900 degrees Celsius. These increased temperatures limit the maximum load of the engine and lead to shortened component life. It would be desirable to provide a readily ignitable fuel mixture in the combustion prechamber and maintain reduced temperatures during the ignition process.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method for providing a hydrogen enriched fuel to a combustion prechamber is disclosed. The method includes reforming a quantity of fuel to produce a hydrogen enriched fuel, delivering the reformed fuel to the combustion prechamber, and combining the hydrogen enriched fuel with a fuel/air mixture to less than stoichiometric.
In another aspect of the present invention a method for providing a reduced temperature ignition in a combustion prechamber is disclosed. The method includes reforming a quantity of fuel to produce a hydrogen enriched fuel, delivering the reformed fuel to the combustion prechamber, delivering a portion of fuel/air mixture from a main combustion chamber to the combustion prechamber, the reformed fuel and the fuel/air mixture combining to less than stoichiometric, and igniting the combined fuel in the combustion prechamber, the less than stoichiometric fuel providing a reduced temperature ignition.
In yet another aspect of the present invention an apparatus for providing a hydrogen enriched fuel to a combustion prechamber is disclosed. The apparatus includes a fuel supply and a fuel reformer for receiving a quantity of fuel from the fuel supply and producing a hydrogen enriched fuel, wherein the hydrogen enriched fuel is combined with a fuel/air mixture in the combustion prechamber at less than stoichiometric.